Mycetoma

A mycetoma is a chronic granulomatous infection that usually involves the lower extremities but may occur in any part of the body. The infection is characterized by swelling, purplish discoloration, tumorlike deformities of the subcutaneous tissue, and multiple sinus tracts that drain pus containing yellow, white, red, or black granules. The color of the granules is partly due to the type of infecting organism. The infection gradually progresses to involve the bone, muscle, or other contiguous tissue and ultimately requires amputation in most progressive cases. Dissemination of the organism may occur but is uncommon. Mycetomas usually are seen among people living in tropical and subtropical regions of the world whose outdoor occupations and failure to wear protective clothing predispose them to trauma.

Two types of mycetomas have been described. Actinomycotic (bacterial) mycetomas are caused by the aerobic actinomycetes, including Nocardia, Actinomadura, and Streptomyces spp. (The aerobic Actinomycetes are described in detail in Chapter 19.) Eumycotic (fungal) mycetomas are caused by a heterogeneous group of fungi that have septate hyphae. Eumycotic mycetomas are subcategorized as white grain mycetomas or black grain mycetomas, a distinction determined by the pigmentation of the infecting agent’s hyphae.

Some hyaline septate molds can cause mycetomas; however, the disease is covered in this section because many of the etiologic agents are dematiaceous fungi. Etiologic agents of eumycotic mycetoma to be discussed include Pseudallescheria boydii and Acremonium spp., causative agents of white grain mycetomas, and Exophiala jeanselmei, Curvularia spp., and Madurella mycetomatis, causative agents of black grain mycetomas.

Most patients with mycetomas live in tropical regions, but infections can occur in temperate zones. The most common etiologic agent of white grain mycetoma in the United States is P. boydii, a member of the Ascomycota. The organism is commonly found in soil, standing water, and sewage; humans acquire the infection through traumatic implantation of the organism into the skin and subcutaneous tissues.

Chromoblastomycosis

Chromoblastomycosis is a chronic fungal infection acquired through traumatic inoculation of an organism, primarily into the skin and subcutaneous tissue. The infection is characterized by the development of a papule at the site of the traumatic insult that slowly spreads to form warty or tumorlike lesions characterized as resembling cauliflower. Secondary infection and ulceration may occur. The lesions usually are confined to the feet and legs but may involve the head, face, neck, and other body surfaces.

Histologic examination of the lesion reveals characteristic sclerotic bodies, which are copper-colored, septate cells that appear to be dividing by binary fission and are thought by some to resemble copper pennies. These infections cause hyperplasia of the epidermis of the skin, which may be mistaken for squamous cell carcinoma. Fungal brain abscess, known in the past as cerebral chromoblastomycosis, may be caused by the dematiaceous fungi; however, it is more appropriately considered a type of phaeohyphomycosis and is discussed with that disease. Chromoblastomycosis is widely distributed, but most cases occur in tropical and subtropical areas of the world. Occasional cases are reported from temperate zones, including the United States. The infection is seen most often in areas in which agricultural workers do not wear protective clothing and suffer thorn or splinter puncture wounds.

Phaeohyphomycosis

Phaeohyphomycosis is a general term used to describe any infection caused by a dematiaceous organism; it includes molds; brownish, yeastlike cells; pseudohyphae; and hyphae, except those described previously. These infections may be subcutaneous, localized, or systemic, and they may be caused by a number of dematiaceous fungi. They include phaeohyphomycotic cysts, progressive soft tissue infection, brain abscess, sinusitis, endocarditis, mycotic keratitis, pulmonary infection, and systemic infection.

Specimen Processing

See General Considerations for the Laboratory Diagnosis of Fungal Infections in Chapter 59.